Polymerizing ethylene in the presence of catalyst consisting of aluminum trialkyl mixed with a solution of a vanadium halide and a titanium halide



March 7, 1967 D. B. LUDLUM 3,308,112

POLYMERIZING ETMYLENE IN THE PRESENCE oF cATALYsT CoNsIsTING 0E ALUMINUM TRIALKYL MIXED wITH A SOLUTION 0F A YANADIUM HALIDE AND A TITANIUM HALIDE Original Filed Deo. 6, 1955 INVENTOR DAVID BLODGETT LUDLUM ATTORNEY Patented Mar. 7, 1967 3,308,112 POLYMERIZING ETHYLENE IN THE PRESENCE F CATALYST CONSISTING 0F ALUMINUM TRIALKYL MIXED WITH A SGLUTION 0F A IA/"IANADIUlVI IDE AND A TITANIUM HA- DE David Blodgett Ludlum, Hamden, Conn., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Continuation of application Ser. No. 390,007, Aug. 17, 1964, now Patent No. 3,218,266, which is a division 0f application Ser. No. 551,389, Dec. 6, 1955. This application Sept. 15, 1965, Ser. No. 487,392

3 Claims. (Cl. 26094.9)

This application is a division of U.S. Patent application Serial No. 390,007, filed August 17, 1964, and now U.S. Patent 3,218,266, which in turn is a continuation of U.S. patent application Serial No. 551,389, filed December 6, 1955, and now abandoned, which application is in turn a continuation-in-part of U.S. patent application Serial No. 520,112, filed July 5, 1955, and now abandoned.

This invention relates to polymerization of alpha oletins, espectially ethylene, higher alkenes, phenyl alkenes, and the like.

It was known heretofore that catalyst systems obtained by admixing a vanadium or titanium halide with a compound having aluminum directly attached to at least one hydrocarbon group, are effective in the polymerization of ethylene to form linear high density polymer at relatively low pressures.

It has now been discovered, in accordance with the present invention, that catalysts formed by admixing a vanadium compound with a titanium halide, and with a compound having a metal (such as aluminum) attached to --H or at least one hydrocarbon group, are more active as polymerization catalysts, than the aforesaid previously known catalyst systems, the increased activity being the result of a synergistic influence exerted by the combination of the vanadium component with the titanium component.

It is noteworthy that vanadium halide-aluminum trialkyl catalysts are generally much more active than titanium halide-aluminum trialkyl catalysts. In fact, the catalyst complex from one mol of titanium tetrachloride has an initial activity equal to that from one twenty-fifth of a mol of vanadium tetrachloride. Nevertheless, the extraordinary activity of the catalysts of the present invention does not merely reiiect the additive effect of highly active vanadium. Instead, the activity is the result of a synergism between the vanadium and titanium components, the theoretical explanation for which is still in doubt.

The presence of a vanadium component in combination with the titanium tetrachloride-aluminum trialkyl catalyst systems employed in ethylene polymerization is reected not only in greatly enhanced initial activity, but also in an overall increase in yield of polymer per unit weight of catalyst, as exemplified hereinafter. The combined components produce high molecular Weight polymer initially, and this is followed by the formation of polymer of a lower molecular weight range as the polymerization progresses. An important advantage of the invention resides in the production of increased yields at desired levels of molecular Weight.

The mixing of the catalyst components may be carried out at any temperature, preferably within the range of 0 to 300 C. The polymerization can be conducted at any temperature within this range or even'at a much lower temperature. The catalysts are active at temperatures as low as 80 C. Pressure is preferably within the range of 1 to 200 atmospheres, but higher or lower pressures can quite readily be employed.

Any quantity of catalyst and liquid medium may lbe employed, the rate of formation of product being of course dependent on the quantity of catalyst. The number of mols of reducing component should preferably be sufficient to reduce the valence of the Ti and/ or V, at least in part to two.

The catalysts of this invention are preferably prepared in an inert hydrocarbon medium, such as decahydronaphthalene, cyclohexane, benzene, etc. The titanium is preferably added in the form of TiCl4, or other form which is soluble in inert hydrocarbon solvents or is a precursor of a form which is soluble in inert hydrocarbon solvents. Other titanium halides may be employed, including those containing alkoxy groups, such as Ti(O alkyl)2Cl2. The Vanadium may be introduced in the form of VCl4, or other halide, such as VOCl3 or in `any form which is soluble in the hydrocarbon medium or is a precursor of a hydrocarbon soluble form. Moreover, the vanadium may be introduced in any form which can produce a vanadium halide by metathesis, such as `ammonium vanadate. A suitable salt such as ammonium vanadate can be added to TlCl4 prior to dissolving the latter in the hydrocarbon medium, to produce an effective catalyst mixture. In certain embodiments, the quantity of vanadium is extremely minute.

The order of addition of the reducing component to the reducible components is critical, if optimum results are to be achieved. The reducing agent can be added to the mixed halides, but the mixed halides should not be added to the reducing agent, to obtain optimum results. However, the synergistic effect is also observed, when the opposite order of addition is used. The vanadium component can be added before or after the addition of the titanium component, but it is preferred to reduce both components simultaneously, as thisgives the best result. Separate streams of halide and reducing agent can be united to produce an effective combined catalyst. It is desirable, however, to avoid too large an excess of reducing agent at the time when the initial mixing takes place, and this can be achieved by joining the streams, or by introducing the solution of reducing agent into the solution of halides rather than by adding the ingredients in the reverse order.

When the ratio of vanadium to titanium is high, the catalysts are more active than the catalysts containing no titanium. When the ratio of vanadium to titanium is very low, the catalysts are more active than those containing no vanadium.

In Examples I-V described below, the solution containing titanium tetrachloride is saturated with ethylene prior to reduction with the aluminum alkyl. This introduction of ethylene prior to introduction of the reducing agent is not particularly critical, and in certain embodiments, it is desirable to carry out the reduction prior to introducing the ethylene.

The invention is further illustrated by means of the following examples:

Example I A solution of aluminum trihexyl in decahydronaphthalene was prepared, the aluminum trihexyl content being 180 micromols per 4.5 ml. A solution of vanadium tetrachloride in decahydronaphthalene was also prepared, the content of vanadium tetrachloride being 3 micromols per 1.0 ml. A third solution, consisting of 45 micromols titanium tetrachloride per 1.0 ml. was also prepared. To ml. decahydronaphthalene was added 1.0 ml. of the titanium tetrachloride solution and the resulting mixture was saturated with ethylene at 100 C., at atmospheric pressure. Using a closed system, 4.5 ml. of the aluminum trialkyl solution was introduced into the liquid reaction mixture, and the mixture was agitated, ethylene absorption at atmospheric pressure being determined quantitatively. The initial rate of ethylene absorption (which corresponds with the rate of polymerization) was 25 ml. per minute. After 140 minutes, the rate had dropped to 1 rnl. per minute, and the total volume of ethylene absorbed was 540 ml. In a parallel experiment 1.0 ml. of the vanadium tetrachloride solution (3 micromols) was employed in place of the titanium tetrachloride. This resulted in an initial rate of 50 ml. per minute, which, however, dropped off to less than 0.3 ml. per minute when the reaction time had reached 140 minutes. At that time the total quantity of ethylene absorbed was 230 ml. A mixture made by adding 3 micromols of vanadium tetrachloride (1.0 ml. of the vanadium solution prepared as above) and 45 micromols titanium tetrachloride (l.0 ml. of the titanium solution), all other conditions including the quantity of aluminum trihexyl being unchanged, gave an initial rate of 50 ml. per minute; the rate was somewhat greater than 5 ml. per minute after 140 minutes, and the total quantity of ethylene absorbed at that time was 1520 ml. The quantity of polymer produced in the latter experiment was large enough to form a gel, and this contributed to a decrease in rate of polymer after such gel was formed.

Example II A solution containing 21 micromols vanadium tetrachloride and 9 micromols titanium tetrachloride in about 100 ml. decahydronaphthalene was saturated with ethylene. The reaction system was connected with a source of ethylene, and with facilities for maintaining the pressure constant at one atmosphere. Also, equipment was provided for measuring rate of absorption of ethylene. The temperature of the reaction mixture was maintained at 100 C. Upon the introduction of 80 micromols aluminum trihexyl (in decahydronaphthalene at same concentration as Example I), measurement of rate of ethylene absorption was commenced. The initial rate was 180 ml. per minute. After 75 minutes, the rate was 5 ml. per minute, and a total of 1620 ml. had been absorbed, a corresponding quantity of polyethylene having been formed.

Example III A solution containing 6 micromols VOC13 and 45 micromols titanium tetrachloride in about 100 ml. decahydronaphthalene was saturated with ethylene. The reaction system was maintained at 100 C. and was kept closed, there being provision for measurement of rate of absorption of ethylene at atmospheric pressure, as in Examples I and II. Upon the introduction of 180 micromols of aluminum trihexyl (in decahydronaphthalene at same concentration as Example I), measurement of rate of ethylene absorption was commenced. The initial rate was 100 ml. per minute. After 120 minutes, the rate was 5 ml. per minute, and the total volume of ethylene polymerized was 1800 ml. In a parallel experiment using the same source of titanium tetrachloride (differing, however, from that of Example I), but with no VOC13 added, the initial rate was 54 ml. per minute. The volume polymerized after 120 minutes was 1150 ml., and the absorption rate was 1 ml. per minute. In another parallel experiment, using the same quantity of VOC13, but no titanium tetrachloride, the initial rate was 21 ml. per minute. After 120 minutes, the total volume of ethylene absorbed was 275 ml., and at that time the ethylene absorption rate had decreased to zero.

Example IV Using the technique described in the preceding examples ethylene was polymerized at 100 C., atmospheric pressure, the catalyst components being 45 micromols titanium tetrachloride, no added vanadium compound and 97 micromols of LiAl(heptyl)4. The initial rate of ethyl- 4. ene absorption (polymerization) was 19 ml. per minute. After 120 minutes, ethylene absorption totaled 215 ml., and at that time the rate of absorption was less than 0.5 ml. per minute. The experiment was repeated, using 3 micromols of vanadium tetrachloride in place of 45 micromols of titanium tetrachloride. The rate of absorption was less than 0.5 ml. per minute. The experiment was repeated using, in addition to 3 micromols of vanadium tetrachloride, 45 micromols of titanium tetrachloride, the same quantity yof LiAl(heptyl)4 being used in all of these runs. The initial rate of ethylene absorption was 55 ml. per minute, and after 120 minutes, the total volume absorbed and converted to polymer was 685 ml. The rate of absorption at that time was 2 ml. per minute.

Example V Using the technique described in the preceding example, ethylene was polymerized at 100 C., atmospheric pressure, the catalyst components being 45 micromols titanium tetrachloride, 9 micromols VO(O-isopropyl)3, 180 micromols aluminum trihexyl in ca. 100 ml. decahydronaphthalene. The initial rate of polymerization was 40 ml. per minute, and after 120y minutes, the rate was 5 ml. per minute, the total volume of ethylene polymerized at that time being 1830 ml. In a parallel run, in which the TiCl4 was omitted, all other ingredients being the same, the initial rate was only 4 ml. per minute, and after 120 minutes the rate had dropped to zero. The total volume of ethylene absorbed was only 20 ml.

Example VI Into a 330 ml. stainless steel shaker tube flushed with nitrogen was added a solution consisting of 0.02 mol LiAlH4, 0.01 mol titanium tetrachloride, 0.01 mol vanadium tetrachloride, 0.24 mol cyclohexene and 100 ml. cyclohexane. After sealing and cooling the tube, it was alternately evacuated and flushed with nitrogen to insure a 100% nitrogen atmosphere. The tube was heated at 100 C. for 10 minutes under autogenous pressure. Thereupon, 20 grams of ethylene were added and the temperature was maintained at 100 for an additional 45 minutes. The tube was cooled, discharged, and the contents were worked up by stirring in a Waring Blendor with acetone until the polymer was white. The resulting mixture was iiltered and the polymer was dried. The weight of dried product was 13.5 grams, the melt index being 5.4 at 190 C.

Example VII A catalyst mixture was prepared by adding 0.05 mol equivalents tin tetra-butyl to 0.01 mol equivalents titanium tetrachloride and 0.01 mol equivalents of vanadium tetrachloride in dry toluene solution. Ethylene was polymerized in the presence of this catalyst at 100 pounds per square inch of pressure. During the course of the reaction, temperature was permitted to rise from 100 C. to 200 C., which caused the pressure to rise to a maximum of 1200 pounds per square inch. The melt index was too low for measurement under standard conditions of testing, but was 0.2 at 190 when measured under an extra load (5 kg.). This indicates very high molecular weight. Similar runs in which the vanadium component and the titanium component were omitted, respectively, gave polymers which had measurable, though low, melt indexes without extra load.

Example VIII Into a continuous reactor having a capacity of one gallon was continuously fed 45 pounds of cyclohexane per hour, containing a catalyst formed from 0.222 millimol of TiCl4-|-VOCl3(Ti/V mol ratio=4/ 1) and aluminum tri-isobutyl (Al/ (Ti-l-V) mol ratio=2/1). With thecyclohexane was also introduced 8.3 pounds per hour of ethylene. Pressure was maintained at 2500 pounds per square inch, by means of a suitable outlet valve through 5. which the product was withdrawn. The solvent was flashed from the resulting mixture by releasing pressure, leaving polyethylene as flulf. When the temperature in the reaction zone was maintained at 255 C. the poly- 6 times the" number of millimols per liter set forth in the tables); catalyst feed tubes 9 for combining a stream drawn from the vessel containing the Ti component with a stream from the vessel containing V component, a tube ethylene thus formed had a melt index of 2i0.5; when 5 10 for introducing into this combined stream a stream, the temperature was raised to 265, the polyethylene had contained in a tube 11 from the vessel 8, and containing a melt index of 3.5. The rate of production Was 339,000 the aluminum trialkyl component, the resulting reaction pounds per pound mol of Ti-l-V. The ash content of product being fed into the reaction vessel through the dip the polymer was extremely low (about 115 p.p.m.) withtube 3. In this apparatus, the reaction between the aluout any alcoholysis or other further treatment. 10 minum alkyl and the reducible catalyst components was in each instance completed in the feed tube prior to entry Example IX of the combined mixture into the polymerization zone through the dip tube. The rates of feed in the respective A atalystl mtfe gazs olitamedly em bewg feed lines were adjusted to produce the quantities of the mlcromos .1 4. mlcronlo O 4 aub l5 respective components set forth in the tables, and the mlcromols of LlAlUsobutyUsCl l? 100 m1' deca ydro' temperature, pressure and rate of throughput were also lliphthalne at 100 C'. (ethylene b ankeo Ethylene as adjusted to the levels listed in the tables. The polymerimlected Into tle resllltlpg mlxture and lldwls follllnd ldzlt zation was performed continuously. The outlet stream a 12 of 1 by y l q h weight methanol per 60 parts of outlet stream). This miles of TICL* and VCLf respecllve y upon reactlon Wil was not sufficient to precipitate polymer, temperature be- L1A1(C4H9?3C1` (Note Tlhe L1A1(a1ky.1)3cl emp10yed-m ing still at the reaction temperature level. Pressure was these experiment? las Obtained by reactlol? betwen equlv' let down by means of the outlet valve 5 to 1 atmosphere, fllent quan/[mes hthmm lsobutlll and {dummum tnchlofle and the solvent was thus ilashed otf and recovered 13, m decahydromlpllthalene Thls .reactlon produced. aw ne the product being collected as a solid (fluif) in a suitpowdery precipitate of 111A1(1S0buty1)3c1 Whlch was able receiver 14. The product was substantially dry, but separated and red1spersed 1n decahydronaphthalene.) Contained au of the Hash., formed from he catalyst. To Example X eliminate ash the product fluff was slurried 15 with methanol in the absence of moisture at room temperature Thirteen experiments were made under conditions set for about one-half hour, The alcohol reacted with the forth in the following tables Using an apparatus such as ash forming alcohol-semble material which was washed that illustrated in 'ille drawing, Comprising a Pressure away with more methanol. The product was dried 15 resistant vessel 1, an inlet tube 2 at the bottom for introin a current of warm air, which resulted in clear White duction of a cyclohexane-ethylene mixture, a dip tube 3 low ash product (ash content reduced to about oneeXfefldlUg from the tOP 0f the Vessel 1 '0 the lOWer p0r- 35 third of its original ash content, i.e. to a few hundred tion thereof, an outlet tube 4 near the top of the vessel p pm, 0r less), The methanol can be recovered by re- 1 equipped with a suitable outlet valve 5; another Vessel distillation if desired 17. (Note: If it is desired to corn- 6 containing a solution of TiCl4 in cyclohexane (conpletely eliminate ash, this can be done by increasing the centration being ten times the number of millimols per 40 quantity of methanol introduced into the hot effluent liter set forth in the tables which follow); another vessel 7 containing a solution of vanadium halide (VC14 or VOC13, as stated in the tables, the concentration being ten times the number of millimols per liter set forth in the tables) in cyclohexane; still another vessel 8 containing under pressure to such an extent that a separate phase 0f molten polyethylene is precipitated, and withdrawing this molten phase of ashfree product. The latter operation can be performed in any suitable vessel adapted for separation of liquid phases at superatmospheric presaluminum tri-isobutyl in cyclohexane (concentration ten sure.)

TABLE I.-SYNERGISTIC EFFECT OF VANADIUM COMPOUNDS ON TiC14-Al(i-Bu)3 SYSTEM Run No 1 2 3 4 5 6 7 8 T1014, mM./1., in polymerization zone 0. 57 3. 38 5. 78 0.225 0. 265 0.13 0.375 VO C13, mM./1., 1n polymerization zone 0. 265 0. 025 0. 085 0. 13 V014, mM./l., in polymerization zone. 0.125 Ratio, Ti/V 9 3 1 3 A1(1Bu)3, mMJl. in polymerization zon 0. 70 3. 22 3. 37 0. 43 0.35 0. 47 0. 36 0.685 Rat1o, .Ae/(T1 and/or V) 1. 21 0. 93 0.58 1.62 1. 40 136 1. 40 1.37 Temperature, C 211 240 210 242 240 245 248 250 Pressure, atm 54 54 54 75 75 75 75 75 Wt. ramo cyelohexane/ethylene in feed 7. 5 13. 4 11. 2 14. 4 9. 1 5. 7 10. 6 7. 6 Conversion of ethylene, percent 53 18 18 55 50 74 83 74 Lbs. eed/hrJl. reactor volume 0.71 0. 13 0. 15 0.39 0. 48 1. 3 0. 91 0. 91 Y1eld lbs. 103 polymer/lb. mole (Ti and/or V) 95 19. 4 12. 2 115 148 294 250 141 Melt man 0. 17 3. 1 19. 5 0.71 1. 7 3.8 10.0 2. 7

TABLE II.SYNERGISTI C EFFECT OF VANADIUM COMPOUNDS ON Ti(0 Run Nn 9 10 11 12 13 Ti(Oi-Pr)z, C12, mM./l., in polymerization zone 0.59 0.51 1.70 0.45 0.375 V014, mM./l., in polymerization 7mm 0. 05 0. 125 Ratio, Ti/V 9 3 Al(i7B11)3, mMJl., in polymerization zone 0.70 0. 68 3. 27 0.68 0.76 Ratio, Al/(Tl and/0r V) 1. 22 1. 30 2. 02 1. 47 1. 52 Temperature, C 240 242 220 244 241 Pressure, atm 54 75 54 75 75 Wt. ratio cyclohexane/ethylene in. feed 16. l 16.1 11. 2 7. 3 8. 9 Conversion of ethylene, percent 26. 7 28. 5 31 53 64 Lbs. feed/lnz/I. reactor volume 0. 17 0. 17 0. 17 0.67 0. 76 Y1eld, 1bs. 10-1 polymer/1b. mole (Ti and/or V) 24 27 12.8 107 118 Melt infie? 2. 0 0. 42 5. 3 1. 1 1. 3

As `is apparent from Example V, the vanadium compOnent need not contain halogen as introduced into the reaction vessel. It is advantageous that the vanadium component be soluble to some extent in the reaction mixture, however. In fact, both the vanadium and titanium should be at least partially dissolved, in the sense that certain compounds having inorganic components are regarded as being capable of solution in organic media. This does not at all imply that the polymerization is necessarily one resulting from purely homogeneous catalysis. The active centers may indeed be on colloidal surfaces, so that even where the catalyst components are soluble, the active catalyst itself may be colloidal, `and the distribution of active catalyst within the mixture, as well as the overall activity of the mixture, can be affected by the high speed ultracentrifuge. Because of such observations as these, it is to be understood that the invention is not limited by any theory as to the nature or explanation of the catalysis, from the standpoint of whether or not the polymerization is initiated by active centers on solid colloidal surfaces.

It is to be understood also that the foregoing examples are illustrative only and that numerous embodiments of the invention will occur lto those who are skilled in the art. For example, other metal alkyls or other compounds having metal attached to an organic group through a metal-carbon bond, besides those illustrated in the examples may be employed. The choice of metal alkyl for best results depends upon the conditions. At relatively high temperatures, metal alkyls which are comparatively weak reducing agents, i.e. aluminum trialkyls, are excellent, while at lower temperatures somewhat stronger reducing agents, such as lithium alkyls, can be used effectively. These stronger reducing agents should preferably not be combined with reducible components which are reduced with great ease at elevated temperatures, for optimum-results. At very low temperatures, the latter combinations are effective.

While the synergistic action is observed over a wide range of temperatures, as hereinabove set forth, it is especially pronounced at temperatures high enough to produce a solution of the polymer, e.g. 100 C., or higher.

It should be noted that the synergistic effect is reflected in the yield of polyethylene per unit weight of catalyst, and in the surprisingly high yields achieved at levels of melt index which prior to the present invention were regarded as associated with much lower yields. For example, at a melt index of 3.1 the TiCl4-Al(isobutyl)3 catalyst system produces about 19,400 pounds of polyethylene per mol pound of catalyst, while a 3/1 mixture of TiCl4 and VCL, with Al(isobutyl)3 yields 141,000 pounds of polymer per pound mol of (Ti-l-V), at a melt index of 2.7. In contrast with this, at a melt index of 0.17, the TiCl4--Al(isobutyl)3 system is capable of giving yields of about 100,000 pounds of polymer per pound mol of Ti, or in particular instances even higher yields. In other words, the improvement is more pronounced at moderate molecular weight ranges (melt index, from l to 5) than at extremely high molecular weight ranges (melt index below 1). The present invention is thus of great value in the manufacture of linear polyethylene which is readily extrudable, i.e. which is not of excessively low melt index, at high yields, exceeding 140,000 pounds per pound mol of catalyst. This is a result which was not attainable heretofore. Another important useful ad- Vantage of the present invention, as applied to the production of polyethylene in solution, is that it permits the` manufacture of solution polymer Which is free of grease Still another important useful advantage which results from the greater yields is the lowering of catalyst cost, and the cost of producing polymer which is virtually free of impurity derived from the catalyst. The latter advantage is especially significant in connection With the use of catalyst components which are effective in production of highly desirable grease-free polymer, but which are relatively expensive (eg. LiAl alkyll).

The catalysts obtained by the method herein disclosed are eiective for polymerization of alpha olenic cornpounds generally, such as alpha olefinic hydrocarbons, vinyl compounds vinylidene compounds, and the like.

While, in the foregoing description, the transition elements present in the catalysts are limited to vanadium and titanium, it is to be understood that other transition elements may, in specic embodiments, also be present in the form of their compounds. These elements, arranged approximately in the order of the activity of their compounds in catalysts of the type herein disclosed are: V, Ti, Nb, Zr, Mo, Cr, Ta, W, Th, Ce, Mn, and Hf. Any of the possible combinations of these compounds may be employed in catalysts based on the synergism which has been discovered in accordance With this invention.

I claim:

1. A polymerization process which comprises contacting ethylene with a catalyst prepared by combining streams containing (1) an aluminum trialkyl and (2) a solution of TiCl4 and a vanadium chloride selected from the group consisting of VC14 and VOCl3 in an inert liquid hydrocarbon medium, and recovering linear polyethylene.

2. The process of claim 1 wherein the temperature at which the ethylene is contacted with the catalyst is in the range of to 300 C. and the pressure is within the range of 1 to 200 atmospheres.

3. A polymerization process which comprises contacting ethylene with a catalyst prepared by mixing an aluminum trialkyl with a solution of TiCl4 and a vanadium chloride selected from the group consisting of VC14 and VOC13 in an inert liquid hydrocarbon medium, and recovering linear polyethylene.

No references cited.

JOSEPH L. SCHOFER, Primary Examiner.

M. B. KURTZMAN, Assistant Examiner. 

1. A POLYMERIZATION PROCESS WHICH COMPRISES CONTACTING ETHYLENE WITH A CATALYST PREPARED BY COMBINING STREAMS CONTAINING (1) AN ALUMINUM TRIALKYL AND (2) A SOLUTION OF TICL4 AND A VANADIUM CHLORIDE SELECTED FROM 